Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by IC engines. Conventional exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) catalyst to convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O) in the presence of ammonia (NH3).
Dual-fuel engines can operate on multiple fuels, for example, diesel, natural gas and/or a mixture thereof. When operating in dual-fuel mode under lean conditions, for example on a mixture of diesel and natural gas, the dual-fuel engine emits a higher quantity of unburnt short-chain hydrocarbons such as methane, ethane, propane etc. in the engine exhaust gas. This requires the aftertreatment system to reduce short-chain saturated hydrocarbon during the dual-fuel mode to meet stringent emission regulations (e.g., Tier 4 emission regulations). Such aftertreatment systems often include a diesel oxidation catalyst (DOC) which can include a platinum (Pt) group DOC, for example a palladium (Pd) based DOC. The Pd DOC tends to oxidize at the high temperature of the exhaust gas to convert to palladium oxide (e.g., PdO and PdO2).
While a certain stoichiometric ratio of Pd:Pd Oxides provides optimal catalytic conversion efficiency, shifting of the stoichiometric ratio of the catalyst towards Pd oxides can degrade the catalyst. The performance of such Pd based catalysts degrades with time both in non-sulfated and sulfated exhaust gases. Furthermore, the water content of the exhaust gas emitted by the engine operating in dual-fuel mode is higher (e.g., 12% of the exhaust gas volume) relative to the water content of the exhaust gas emitted by the engine while operating on diesel only (e.g., 8% of the exhaust gas volume), which also can contribute to oxidation of the Pd catalyst.